Generally, frictional resistance of water is exerted on a submerged outer surface of a bottom of a sailing ship, so that most of ship body resistance is the frictional resistance generated by a relative flow of the water on a ship's bottom. To handle this problem, there has been proposed a technique for reducing the frictional resistance of the ship body by covering an outer surface of the ship body with an air flow when the ship is sailing.
This type of ship-body frictional resistance reducing device is configured by forming an opening portion on a ship's bottom, providing an air chamber in an opening portion, forming a large number of air ejection holes in the air chamber, and connecting an air supply pipe from a compressor to the air chamber. Therefore, when air is supplied to the air chamber through the air supply pipe by the compressor, the air is ejected from a large number of the air ejection holes to cover the outer surface of the ship body with an air bubble curtain, by which the frictional resistance of the water exerted on the outer surface of the ship body can be reduced.
Although the outer surface of the ship body is covered with the air bubble curtain by ejecting the air from the bottom of the ship body during the ship is sailing, the ejection of the air from the bottom of the ship body is stopped while the ship is at anchor. Therefore, there can be a case that sea water intrudes into the air chamber through a large number of the air ejection holes, and marine species such as shellfishes or seaweeds adhere to the air ejection holes and the like, and may block the air ejection holes.
To handle this problem, as a measure for preventing adhesion of marine species to air ejection holes of a ship body in a ship-body frictional resistance reducing device, for example, there is a technique described in Patent Document 1 mentioned below. In the ship-body frictional resistance reducing device described in Patent Document 1, the air ejection holes are prevented from being blocked by creating a condition that is avoided by marine species by blowing a chlorine gas into the air ejection holes.
Patent Document 1: Japanese Patent Application Laid-open No. H11-310188